What is an options chain and how to read one

An options chain is just a structured price list. For a given stock or index, it shows every available expiration and every strike. The convention is calls on the left half, puts on the right half, with strike prices descending or ascending down the middle.

The columns you need to read, ignoring everything else:

Bid and ask are what someone will pay or sell to you at right now. The mark is the midpoint, which is what brokers usually quote. Spreads matter — wide spreads (>10% of mark) mean illiquid contracts you should avoid unless you have a specific reason.

Implied volatility (IV) is the option's annualised volatility expectation. Compare IV across strikes: a smile (IV high at the wings, low at the money) is normal for stocks; a smirk skewed to puts is fear of a downside event. Compare IV across expirations: term structure inversion (front-month IV > back-month IV) usually means an earnings or macro catalyst is dated.

Open interest (OI) is the number of contracts currently outstanding at that strike. Volume is contracts traded today. The strikes with the highest OI are where dealer hedging is most concentrated — moves into and through those strikes tend to be sharp.

Delta is the option's price sensitivity to a $1 move in the underlying. A delta of 0.50 means the option moves about $0.50 for every $1 in the underlying. It is also the rough probability that the option finishes in the money at expiration, which is a useful sanity check on whether your strike is a reasonable bet.

For a practical worked example, look at the chain for NVDA on any options broker before earnings — you'll see the front-month IV spike, the term structure invert, and the put OI concentrate at strikes 5-10% below spot. That is the textbook earnings setup.